The present invention relates to a support structure for a roof of an accomodation for cultivation, in particular a green house, comprising posts lined up in rows for supporting a roof structure, the posts being provided with cross beams for bracing said support structure.
These types of support structures are known per se and between the individual roof sections, a gutter is provided in the roof structure, said gutter being supported by posts lined up in rows. In each row the posts are disposed at a distance of 3-3.20 meters from each other, whereas the distance between two rows of posts, i.e. the posts for a neighboring gutter, amounts to approximately 6-6.40 meters. The posts are then lined up in a quadrangle, that is, all first posts of each row underneath a gutter, are also part of a row running in a direction transverse to the original row. This likewise applies to the second and subsequent posts of each row. Each cultivating section in the accomodation for cultivation is so formed between two rows of posts under a roof section. A large number of rows of posts can thus be juxtaposed. So as to obtain a bracing in the roof structure, the gutter on the posts has a certain strength, possibly improved by auxiliary struts. In order to bridge the great width of the cultivating area, purlins are provided which are called lattice girders and which are located between all first posts of each row as well as between the subsequent posts of the rows. Each lattice girder consists of an upper and a lower purlin joined to one another by a diagonal joint. The end of each lattice girder is mounted to the side of a post. On the top of the lattice girder there are provided supporting poles or tie rods adapted to support and/or wind-brace the roof. The underside of the lattice girder serves the suspend the cultivating lines, spraying ducts, etc.
Since nowadays sun blinds are being used in the cultivating area which are in the form of horizontally running curtains, it is not possible to properly support these blinds, as the top side of each lattice girder is connected to the roof structure and the underside is provided with cultivating lines or spraying ducts.
In order, none the less, to be able to use sun blinds, there is provided underneath the lattice girder a second purlin which is called energy girder. The underside of said energy girder is provided with the usual cultivating wires, spraying ducts, etc., whereas the top side of the energy girder serves to support the sun blinds. Usually, enough space is available underneath the gutters of the roof structure to enable the use of a good, strong support structure in relation to the dimensions of the posts; also, the gutters may be of such a rigid form that a relatively great length can be bridged. Thus, the distance between two neighboring posts in a row can be easily doubled, for example up to a distance of 6-6.40 meters, with less cast shadow occurring.
Thus far, enlarging the distance between the posts in a row has been hardly feasible, because there would arise too great a distance between the lattice girders.